1. Field of the Invention
This invention relates generally to the art of pipeline repair, and more particularly to a device for cutting accurately placed and shaped lateral outlets in the liner of an underground pipeline, such as sewer pipe.
2. Description of the Prior Art
Various techniques are known for lining sewer pipes and other buried fluid conduits, when they have developed leaks. In one such method, a long length of cuffed polyethylene tubing is everted as it is pushed into the pipe, covering the interior surface of the pipe with an unbroken plastic lining. The task then remains of cutting lateral outlets in the lining, at positions exactly corresponding to the existing lateral taps on the original pipe, which may be of cast iron or clay.
The devices disclosed in prior patents appear satisfactory to cut holes through pipe linings, once the proper location of the hole has been determined. But before a lateral outlet can be cut, its proper location must first be identified. Prior inventors have had to rely on pipe surveys conducted before the relining procedure, in order to know exactly, or at least approximately, where to cut the lateral outlets. Surveying errors could thus result in ruining the lining, the existing pipe, and/or the lateral cutting tool.
Some inventors have tackled this problem. For example, U.S. Pat. No. 4,577,388 discloses an apparatus comprising a sled which is pulled through a newly lined pipe. The sled has a TV camera for viewing the pipe or lining, and a rotary cutter mounted for "universal" movement on the sled. The camera and cutter are used first to survey the pipe prior to relining, coordinates of the pipe outlets being stored in memory, and then, after the pipe is relined, to cut holes in the lining at the memorized locations. The position of the cutter may be controlled in two dimensions, whereby non-circular holes can be obtained.
U.S. Pat. No. 4,648,454 also solves the problem of reestablishing lateral connections in a lined pipe, by providing a sled that can be towed through the lining, the sled comprising structure for supporting a rotary cutter which first pierces the lining and then enlarges it, using the preexisting outlet as a template.
Other patents of interest include U.S. Pat. No. 4,197,908, U.S. Pat. No. 4,442,891, U.S. Pat. No. 4,701,988, U.S. Pat. No. 4,819,721, and U.S. Pat. No. 4,630,676.
Non-mechanical methods of locating hidden sewer outlets have included using ultrasonic energy; however, for such a method to work, good acoustical contact is imperative, and this is problematic with a device that moves unattended through underground piping, which may not be free of debris and other acoustic contaminants.
Infrared inspection has also been considered. However, the material from which sewer liner is commonly made is opaque to infrared radiation.
Another problem encountered in cutting holes through pipe liners is that, particularly where a lateral pipe meets the main line at a non-perpendicular angle, their intersection may be substantially non-circular. It is desirable to cut a hole in the liner most closely corresponding with the original hole, so as not to create obstructions. While some prior inventors have addressed this problem, an improved device for cutting non-circular holes is needed.